1. Field of the Invention
The present invention relates to a display device provided with an optical input function for obtaining information from a display screen by using light.
2. Description of the Related Art
In recent years, as a display device used for various devices such as a cellular phone and a laptop computer, a liquid crystal display device is widely used. In a display unit of a liquid crystal display device, a plurality of scan lines and a plurality of signal lines are arranged so that each scan line intersects each signal lines. In addition, pixels, each of which includes a thin film transistor, a liquid crystal capacitance and an auxiliary capacitance, are provided respectively to the intersections. The liquid crystal display device is provided with a drive circuit which drives each scan line and each signal line.
As a display device, which includes photosensors arranged in pixels, and which thereby is capable of obtaining information from a display screen by using light, for example, there is one described in Japanese Patent Application Laid-open Publication No. 2006-91897.
In such a display device, for example, photodiodes are provided as photosensors respectively in pixels, and a capacitor is connected to each of the photodiodes. In the display device, the amount of charge in each of the capacitors is changed according to the amount of light which enters from a display screen, and which is received by the corresponding photodiode. In this state, by detecting voltages on both sides of each of the capacitors, the display device generates data on a picked-up image, and thus captures the image.
As an application of such a display device, a device incorporating a touch panel or a digitizer has been proposed. The touch panel allows a user to input information to the device by detecting a shadow of an object such as a finger, which is projected onto a display screen. The digitizer allows a user to input information to the device by detecting light radiated from an illuminating object, such as a light pen.
However, in the case of such a conventional display device having an optical input function, ambient light conditions such as lighting sometimes makes it difficult to distinguish a case where a finger or the like actually touches a display screen, form a case where the finger or the like is merely in the air above the display screen. This leads to an incorrect input.